Inflatable packers are commonly used in oil well operations where the inflatable packer is disposed on a string of pipe in a well bore at a desired location. An inflation cement slurry or an inflating fluid is introduced through the string of pipe to a valve system in the inflatable packer. The valve system admits the inflating fluid to the interior of an inflatable packer element. The inflating fluid under pressure expands the packer element into sealing contact with the wall of the well bore.
An inflatable packer element of the type contemplated by the present invention typically will be 20 or more feet in length but may be different lengths in some circumstances. Presently, there are available inflatable packers in 3, 7, 10, 20 and 40 feet lengths which are expandable. Longer packers include an elastomer packing element disposed along a central mandrel where the packing element is progressively expandable from the bottom end of the packer element toward the top end. An inflation valve system is located at the upper end of the packer. If it is desired to run closely coupled inflatable packers, that is, two packers connected end to end or close relationship to one another, a problem can arise if the well bore is impervious, i.e. a casing or a hard rock formation. The inflation of the packer element creates a low volume annular space between the adjacent ends of the packer elements. The packer elements compress the liquid in the annular space and the trapped pressure can increase to a point to cause damage to the formations, the packer elements, and/or the mandrel itself. In certain instances a single packer can be set in a location near the bottom of a well bore where trapped pressure can create an adverse effect.
In still another instance of use, if an inflatable packer is set with one end of the packer element located in an enlarged or washed out section of the bore, damage can occur when the inflation of the packer element occurs in the washed out section. When a packer element is expanded in a washed out section, the element may burst if the inflation pressure rating of the packer is exceeded.
The examples of progressively inflated packer elements may be found in U.S. Pat. No. 4,781,249, issued Nov. 1, 1988; an example of a top mounted inflation valve can be found in U.S. Reissue Pat. No. RE 32345, issued Feb. 3, 1987. An inflation tool for selectively admitting cement slurry to one inflatable packer at a time is found in U.S. Pat. No. 5,082,062, issued Jun. 21, 1992.